This purpose of this K99-R00 Pathway to Independence Award is to expedite the candidate's development into an independent investigator with expertise in the conduct of large-scale behavioral interventions and health communication related to breastfeeding education and support. Within this 5 year award, the first two years (K99 phase) will be dedicated to obtaining the training necessary to accomplish these goals and developing the intervention content to be used in the R00 phase. In the R00 phase (final 3 years of award), the candidate will conduct a study that utilizes the acquired training skills to address maternal perceived insufficient milk (PIM), the most frequent reason for premature breastfeeding cessation. The study will involve a pilot randomized trial of the K99-developed MILK intervention-a mobile, semi-automated text message-based intervention to prevent perceived low or insufficient milk supply, in a population of mothers without prior breastfeeding experience. MILK improves upon existing breastfeeding support interventions through its potential for transferability to other settings, sustainability, and specific focus on IM prevention, rather than post-hoc treatment of individual breastfeeding problems. Automated texts, which comprise the basis of MILK, will include both prenatal and postpartum education and support geared toward prevention of PIM. Messages will be time-sensitive (e.g., specific to gestational age of fetus/infant, time since delivery) and based on the Breastfeeding Self-Efficacy (Social Cognitive) Theory and pilot work undertaken in the K99 phase. The MILK intervention will be trialed against a control intervention group, who will receive more general perinatal education through the national Text4Baby system. Both groups will receive text messages 3-5 times per week from week 25 of pregnancy through week 8 postpartum. Measured outcomes of interest will include perceived breast milk supply, breastfeeding confidence, maternal anxiety, breastfeeding exclusivity, and breastfeeding duration. Data will be collected at baseline (13-25 gestational weeks), 34-36 gestational weeks, and at 1, 2, 4, and 8 weeks postpartum. To assess the potential longer-term impact of the intervention, breastfeeding continuation and exclusivity will be reassessed via telephone at 6 months postpartum. Between group and group x time differences in outcome measures will be examined graphically and via linear mixed modeling. To assess the potential need for modifications to MILK, telephone interviews will be conducted with a subset of participants in each group to assess and compare intervention use, burdens and challenges, and suggested alterations. The results from this R00 study are expected to inform a larger, multisite intervention trial. The proposed MILK intervention is both timely and significant, as it addresses barriers to breastfeeding duration and exclusivity which have been designated national health priorities by Healthy People 2020 and the U.S. Surgeon General. This study also addresses NINR's mission to create innovative communication interventions for individuals and communities that promote health while reducing associated healthcare costs.